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De-Greasing Process

De-Greasing Process


Chemical de-greasing methods used in any particular application is closely related to the nature of the surface being cleaned and the amount and type of contamination.
​The various chemical de-greasing processes applicable to Mild Steel, Galvanised Steel & Aluminum Substrates, are as follows:

  • 1. Solvent Cleaning
  • 2. Emulsion Cleaning
  • 3. Alkali Cleaning

1. Solvent Cleaning

There are 2 methods of Solvent Cleaning:

  • a. Solvent Wipe
  • b. Vapour De-Greasing

a. Solvent Wipe

Solvent cleaning is the cheapest and best method to remove heavy or sticky oil/grease like substances form nay surface. Since all solvents are almost neutral they do not attack to the base metal. In this process, the parts to be cleaned are wiped with rag of cotton soaked in a suitable solvent such as Kerosene, Benzene, Naptha etc.
The following are the advantages and disadvantages of solvent wipe method:

Advantages
  • Cheapest cleaning method available in the industry to remove heavy oils, greases or sticky press compounds.
  • Skilled labours and costly plant installation is not required.
  • Suitable for smallest job coater as well as for OEM industry.

Disadvantages
  • The process is labour intensive.
  • Since all the solvents are flammable, a great fire risk is associated with the solvent cleaning.
  • Frequent change of cloth and solvent is essential or otherwise it can affect the quality of cleaning.
  • Solvent going into the drainage can cause effluent disposal problem.

b. Vapour De-Greasing

Vapour de-greasing is quite a sophisticated method of cleaning. In this method, special type of solvent is used which has following advantages:

  • Mineral & vegetable oils removal is faster.
  • Has lower boiling point than water.
  • Non-toxic to human beings.

This process requires a closed system in which the item to be cleaned is exposed to the condensing vapours of solvent. This method effectively removes light oils, greases but cannot remove heavy oils, greases, and sticky press compounds.
This process has the following advantages and disadvantages:

Advantages
  • Very good method for cleaning light oils and greases.
  • Less risk of fire hazard, minimum pollution as it is a closed system.
  • Since the solvent used is not-toxic, there is no danger for the operating worker.

Disadvantages
  • Requires costly plant installation and skilled labour.
  • Frequent removal of oil & grease is required or otherwise they increase boiling point of the solvent.
  • Thin sheets having heavy oil grease or sticky press compounds can not be removed by the process as there is no mechanical action on the parts.
  • It is a costly process.

2. Emulsion Cleaning

Emulsion cleaners are popular as they are based on mild Alkalis and hence suitable to all substrates (Iron, Galvanised steel Mazak etc.) and operate at room temperature. Emulsion cleaners are generally based on either kerosene-emulsifier or turpentine-emulsifier. These cleaners are generally milky in appearance. Emulsion cleaners have a limited cleaning tendency and they leave a very thin film of solvent/emulsifier over the substrate even after water rinsing. Hence, Emulsion Cleaning is always followed by Alkali cleaning. In case of spray process the parts to be cleaned are suspended in a funner wherein they are constantly exposed to the spray solution for 2 to 5 minutes at a pressure of 2-3 kgs/cm² for better results. In dip process, the parts to be cleaned are simply immersed in a bath of the cleaning solution.
This process has the following advantages and disadvantages:


Advantages
  • Operates at a lower temperature (45-50ºC) hence consumes less energy.
  • Suitable for all the substrates such as Mild steel, Mazak, Aluminium, Galvanised steel etc.

Disadvantages
  • Limited cleaning ability as it can not remove heavy grease, oil etc.
  • Not suitable for higher temp. As the emulsions are based on solvents which gets separated above 70ºC from the emulsion phase.

3. Alkali Cleaning

Alkali cleaners enjoy superior position in the Pre-treatment industry due to following advantages:

  • They operate at room temperature.
  • Bath stability is higher compared to all other de-greasing processes, low foaming tendency.

These cleaners are based on strong alkalies such as Sodium hydroxide, Sodium silicates, other filters and builders such as soda ash etc, surfactants and additives.

The parts to be cleaned are immersed in this bath at a recommended temperature and time.

Strong alkaline cleaners are avoided in case of Manganese phosphate process as they can cause inferior quality coating. Strong alkaline cleaners are also not suitable for non-ferrous substrate such as Zinc, Aluminum, Brass, Copper, Glass, Galvanised Steel, because all these metals readily get attacked by strong alkalies.